IB · PHYSICS SL

Physics: Standard Level

Nuclear and quantum physics — Theme E

Name: ____________________Date: October 10, 2026

1.
A nucleus of uranium-238 (₉₂²³⁸U) decays by emitting an alpha particle. Write the nuclide notation of the resulting daughter nucleus.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that an alpha particle removes mass number 4 and atomic number 2. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: Obtains mass number 234 and atomic number 90. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: Writes the daughter nuclide as ₉₀²³⁴Th (thorium-234). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Both mass number and atomic number must balance across a decay equation.
Marking points
- States that an alpha particle removes mass number 4 and atomic number 2.
- Obtains mass number 234 and atomic number 90.
- Writes the daughter nuclide as ₉₀²³⁴Th (thorium-234).
Examiner tip: Both mass number and atomic number must balance across a decay equation.
2.
Marking analysis: A learner attempts the following task: “A nucleus of uranium-238 (₉₂²³⁸U) decays by emitting an alpha particle. Write the nuclide notation of the resulting daughter nucleus.” Their response addresses only this point: “States that an alpha particle removes mass number 4 and atomic number 2.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that an alpha particle removes mass number 4 and atomic number 2. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Obtains mass number 234 and atomic number 90. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Writes the daughter nuclide as ₉₀²³⁴Th (thorium-234). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that an alpha particle removes mass number 4 and atomic number 2.
- Identifies the missing requirement: Obtains mass number 234 and atomic number 90.
- Identifies the missing requirement: Writes the daughter nuclide as ₉₀²³⁴Th (thorium-234).
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
3.
A radioactive isotope has a half-life of 5 days. A sample starts with an activity of 800 counts per minute. Calculate the activity after 20 days.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Develop this part of the answer: Identifies that 20 days is four half-lives. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: Halves the activity four times: 800 → 400 → 200 → 100 → 50. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States the final activity as 50 counts per minute. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Count how many whole half-lives have passed before halving; do not divide by the number of days directly.
Marking points
- Identifies that 20 days is four half-lives.
- Halves the activity four times: 800 → 400 → 200 → 100 → 50.
- States the final activity as 50 counts per minute.
Examiner tip: Count how many whole half-lives have passed before halving; do not divide by the number of days directly.
4.
Marking analysis: A learner attempts the following task: “A radioactive isotope has a half-life of 5 days. A sample starts with an activity of 800 counts per minute. Calculate the activity after 20 days.” Their response addresses only this point: “Identifies that 20 days is four half-lives.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: Identifies that 20 days is four half-lives. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Halves the activity four times: 800 → 400 → 200 → 100 → 50. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States the final activity as 50 counts per minute. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: Identifies that 20 days is four half-lives.
- Identifies the missing requirement: Halves the activity four times: 800 → 400 → 200 → 100 → 50.
- Identifies the missing requirement: States the final activity as 50 counts per minute.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
5.
Distinguish between alpha, beta and gamma radiation in terms of their penetrating power through materials.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that alpha radiation is stopped by a few centimetres of air or a sheet of paper (least penetrating). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that beta radiation is stopped by a few millimetres of aluminium. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that gamma radiation requires several centimetres of lead to significantly reduce it (most penetrating). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Penetrating power increases in the order alpha < beta < gamma, while ionising power decreases in the same order.
Marking points
- States that alpha radiation is stopped by a few centimetres of air or a sheet of paper (least penetrating).
- States that beta radiation is stopped by a few millimetres of aluminium.
- States that gamma radiation requires several centimetres of lead to significantly reduce it (most penetrating).
Examiner tip: Penetrating power increases in the order alpha < beta < gamma, while ionising power decreases in the same order.
6.
Marking analysis: A learner attempts the following task: “Distinguish between alpha, beta and gamma radiation in terms of their penetrating power through materials.” Their response addresses only this point: “States that alpha radiation is stopped by a few centimetres of air or a sheet of paper (least penetrating).” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that alpha radiation is stopped by a few centimetres of air or a sheet of paper (least penetrating). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that beta radiation is stopped by a few millimetres of aluminium. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that gamma radiation requires several centimetres of lead to significantly reduce it (most penetrating). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that alpha radiation is stopped by a few centimetres of air or a sheet of paper (least penetrating).
- Identifies the missing requirement: States that beta radiation is stopped by a few millimetres of aluminium.
- Identifies the missing requirement: States that gamma radiation requires several centimetres of lead to significantly reduce it (most penetrating).
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
7.
Describe the structure of the atom in terms of the nucleus and electron arrangement, including the relative size of the nucleus compared to the whole atom.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that the atom has a small, dense, positively charged nucleus at its centre, containing protons and neutrons. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that electrons occupy the region around the nucleus at relatively large distances, occupying most of the atom's volume. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that the nucleus is extremely small compared to the overall size of the atom (most of the atom is empty space). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: This nuclear model was established by the Rutherford (gold foil) alpha-scattering experiment, showing most alpha particles passed straight through — evidence that atoms are mostly empty space.
Marking points
- States that the atom has a small, dense, positively charged nucleus at its centre, containing protons and neutrons.
- States that electrons occupy the region around the nucleus at relatively large distances, occupying most of the atom's volume.
- States that the nucleus is extremely small compared to the overall size of the atom (most of the atom is empty space).
Examiner tip: This nuclear model was established by the Rutherford (gold foil) alpha-scattering experiment, showing most alpha particles passed straight through — evidence that atoms are mostly empty space.
8.
Marking analysis: A learner attempts the following task: “Describe the structure of the atom in terms of the nucleus and electron arrangement, including the relative size of the nucleus compared to the whole atom.” Their response addresses only this point: “States that the atom has a small, dense, positively charged nucleus at its centre, containing protons and neutrons.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that the atom has a small, dense, positively charged nucleus at its centre, containing protons and neutrons. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that electrons occupy the region around the nucleus at relatively large distances, occupying most of the atom's volume. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that the nucleus is extremely small compared to the overall size of the atom (most of the atom is empty space). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that the atom has a small, dense, positively charged nucleus at its centre, containing protons and neutrons.
- Identifies the missing requirement: States that electrons occupy the region around the nucleus at relatively large distances, occupying most of the atom's volume.
- Identifies the missing requirement: States that the nucleus is extremely small compared to the overall size of the atom (most of the atom is empty space).
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
9.
Calculate the energy of a photon of light with wavelength 500 nm. Use h = 6.63 × 10⁻³⁴ J s and c = 3.00 × 10⁸ m s⁻¹.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Uses E = hc/λ. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
3. Work through this mathematical step: Substitutes (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(500 × 10⁻⁹). Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
4. Develop this part of the answer: Obtains E ≈ 3.98 × 10⁻¹⁹ J. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Photon energy is inversely proportional to wavelength — shorter-wavelength (e.g. blue/UV) photons carry more energy than longer-wavelength (e.g. red/IR) photons.
Marking points
- Uses E = hc/λ.
- Substitutes (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(500 × 10⁻⁹).
- Obtains E ≈ 3.98 × 10⁻¹⁹ J.
Examiner tip: Photon energy is inversely proportional to wavelength — shorter-wavelength (e.g. blue/UV) photons carry more energy than longer-wavelength (e.g. red/IR) photons.
10.
Marking analysis: A learner attempts the following task: “Calculate the energy of a photon of light with wavelength 500 nm. Use h = 6.63 × 10⁻³⁴ J s and c = 3.00 × 10⁸ m s⁻¹.” Their response addresses only this point: “Uses E = hc/λ.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: Uses E = hc/λ. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Substitutes (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(500 × 10⁻⁹). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Obtains E ≈ 3.98 × 10⁻¹⁹ J. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: Uses E = hc/λ.
- Identifies the missing requirement: Substitutes (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(500 × 10⁻⁹).
- Identifies the missing requirement: Obtains E ≈ 3.98 × 10⁻¹⁹ J.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
11.
Explain the photoelectric effect, and state why it provides evidence for the particle (photon) nature of light.
[4 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that the photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency shines on it. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that emission only occurs above a threshold frequency, and occurs instantaneously, regardless of light intensity. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that this cannot be explained by the wave model of light (which would predict emission at any frequency given enough time/intensity). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Work through this mathematical step: States that it is explained by treating light as photons, each carrying discrete energy E = hf; only a photon with energy above the metal's work function can eject an electron, explaining the threshold frequency and instantaneous emission. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The photoelectric effect is the single most important piece of evidence for the particle (quantum) nature of light, since the wave model cannot explain the threshold frequency or instantaneous emission.
Marking points
- States that the photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency shines on it.
- States that emission only occurs above a threshold frequency, and occurs instantaneously, regardless of light intensity.
- States that this cannot be explained by the wave model of light (which would predict emission at any frequency given enough time/intensity).
- States that it is explained by treating light as photons, each carrying discrete energy E = hf; only a photon with energy above the metal's work function can eject an electron, explaining the threshold frequency and instantaneous emission.
Examiner tip: The photoelectric effect is the single most important piece of evidence for the particle (quantum) nature of light, since the wave model cannot explain the threshold frequency or instantaneous emission.
12.
Marking analysis: A learner attempts the following task: “Explain the photoelectric effect, and state why it provides evidence for the particle (photon) nature of light.” Their response addresses only this point: “States that the photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency shines on it.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that the photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency shines on it. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that emission only occurs above a threshold frequency, and occurs instantaneously, regardless of light intensity. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that this cannot be explained by the wave model of light (which would predict emission at any frequency given enough time/intensity). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: States that it is explained by treating light as photons, each carrying discrete energy E = hf; only a photon with energy above the metal's work function can eject an electron, explaining the threshold frequency and instantaneous emission. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that the photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency shines on it.
- Identifies the missing requirement: States that emission only occurs above a threshold frequency, and occurs instantaneously, regardless of light intensity.
- Identifies the missing requirement: States that this cannot be explained by the wave model of light (which would predict emission at any frequency given enough time/intensity).
- Identifies the missing requirement: States that it is explained by treating light as photons, each carrying discrete energy E = hf; only a photon with energy above the metal's work function can eject an electron, explaining the threshold frequency and instantaneous emission.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
13.
Distinguish between nuclear fission and nuclear fusion, and state one condition required for each to occur.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that fission is the splitting of a large, unstable nucleus into two smaller nuclei, usually triggered by neutron absorption. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that fusion is the combination of two small, light nuclei into one larger nucleus. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that fusion requires extremely high temperature and pressure to overcome the electrostatic repulsion between the positively charged nuclei. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Both fission and fusion release energy because the products have greater binding energy per nucleon than the reactants — this is why both processes are exothermic, despite being opposite in mechanism.
Marking points
- States that fission is the splitting of a large, unstable nucleus into two smaller nuclei, usually triggered by neutron absorption.
- States that fusion is the combination of two small, light nuclei into one larger nucleus.
- States that fusion requires extremely high temperature and pressure to overcome the electrostatic repulsion between the positively charged nuclei.
Examiner tip: Both fission and fusion release energy because the products have greater binding energy per nucleon than the reactants — this is why both processes are exothermic, despite being opposite in mechanism.
14.
Marking analysis: A learner attempts the following task: “Distinguish between nuclear fission and nuclear fusion, and state one condition required for each to occur.” Their response addresses only this point: “States that fission is the splitting of a large, unstable nucleus into two smaller nuclei, usually triggered by neutron absorption.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that fission is the splitting of a large, unstable nucleus into two smaller nuclei, usually triggered by neutron absorption. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that fusion is the combination of two small, light nuclei into one larger nucleus. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that fusion requires extremely high temperature and pressure to overcome the electrostatic repulsion between the positively charged nuclei. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that fission is the splitting of a large, unstable nucleus into two smaller nuclei, usually triggered by neutron absorption.
- Identifies the missing requirement: States that fusion is the combination of two small, light nuclei into one larger nucleus.
- Identifies the missing requirement: States that fusion requires extremely high temperature and pressure to overcome the electrostatic repulsion between the positively charged nuclei.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
15.
Explain how the de Broglie hypothesis extends wave-particle duality to matter, and calculate the de Broglie wavelength of an electron moving at 2.0 × 10⁶ m s⁻¹. Use h = 6.63 × 10⁻³⁴ J s and the electron mass = 9.11 × 10⁻³¹ kg.
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Develop this part of the answer: States that de Broglie proposed that matter, like light, exhibits both particle and wave properties, with an associated wavelength. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Work through this mathematical step: States the de Broglie relation λ = h/(mv) (h/p). Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
4. Work through this mathematical step: Substitutes (6.63 × 10⁻³⁴)/(9.11 × 10⁻³¹ × 2.0 × 10⁶). Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Develop this part of the answer: Obtains λ ≈ 3.64 × 10⁻¹⁰ m. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The de Broglie wavelength is only significant (measurable) for very small masses like electrons — for everyday macroscopic objects, the wavelength is far too small to ever observe.
Marking points
- States that de Broglie proposed that matter, like light, exhibits both particle and wave properties, with an associated wavelength.
- States the de Broglie relation λ = h/(mv) (h/p).
- Substitutes (6.63 × 10⁻³⁴)/(9.11 × 10⁻³¹ × 2.0 × 10⁶).
- Obtains λ ≈ 3.64 × 10⁻¹⁰ m.
Examiner tip: The de Broglie wavelength is only significant (measurable) for very small masses like electrons — for everyday macroscopic objects, the wavelength is far too small to ever observe.
16.
Marking analysis: A learner attempts the following task: “Explain how the de Broglie hypothesis extends wave-particle duality to matter, and calculate the de Broglie wavelength of an electron moving at 2.0 × 10⁶ m s⁻¹. Use h = 6.63 × 10⁻³⁴ J s and the electron mass = 9.11 × 10⁻³¹ kg.” Their response addresses only this point: “States that de Broglie proposed that matter, like light, exhibits both particle and wave properties, with an associated wavelength.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that de Broglie proposed that matter, like light, exhibits both particle and wave properties, with an associated wavelength. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States the de Broglie relation λ = h/(mv) (h/p). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Substitutes (6.63 × 10⁻³⁴)/(9.11 × 10⁻³¹ × 2.0 × 10⁶). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: Obtains λ ≈ 3.64 × 10⁻¹⁰ m. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that de Broglie proposed that matter, like light, exhibits both particle and wave properties, with an associated wavelength.
- Identifies the missing requirement: States the de Broglie relation λ = h/(mv) (h/p).
- Identifies the missing requirement: Substitutes (6.63 × 10⁻³⁴)/(9.11 × 10⁻³¹ × 2.0 × 10⁶).
- Identifies the missing requirement: Obtains λ ≈ 3.64 × 10⁻¹⁰ m.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
17.
Outline the evidence provided by atomic line emission spectra for the existence of discrete (quantised) electron energy levels within an atom.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that an excited atom emits light only at specific, discrete wavelengths (a line spectrum), rather than a continuous range of wavelengths. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that each spectral line corresponds to a photon of a specific energy, emitted when an electron falls from a higher energy level to a lower one. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that since only specific photon energies (and hence wavelengths) are observed, the electron energy levels themselves must be discrete (quantised), not continuous. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Line spectra were the key experimental evidence that led to the Bohr model of the atom, with electrons confined to specific quantised energy levels rather than orbiting at any arbitrary distance.
Marking points
- States that an excited atom emits light only at specific, discrete wavelengths (a line spectrum), rather than a continuous range of wavelengths.
- States that each spectral line corresponds to a photon of a specific energy, emitted when an electron falls from a higher energy level to a lower one.
- States that since only specific photon energies (and hence wavelengths) are observed, the electron energy levels themselves must be discrete (quantised), not continuous.
Examiner tip: Line spectra were the key experimental evidence that led to the Bohr model of the atom, with electrons confined to specific quantised energy levels rather than orbiting at any arbitrary distance.
18.
Marking analysis: A learner attempts the following task: “Outline the evidence provided by atomic line emission spectra for the existence of discrete (quantised) electron energy levels within an atom.” Their response addresses only this point: “States that an excited atom emits light only at specific, discrete wavelengths (a line spectrum), rather than a continuous range of wavelengths.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that an excited atom emits light only at specific, discrete wavelengths (a line spectrum), rather than a continuous range of wavelengths. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that each spectral line corresponds to a photon of a specific energy, emitted when an electron falls from a higher energy level to a lower one. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that since only specific photon energies (and hence wavelengths) are observed, the electron energy levels themselves must be discrete (quantised), not continuous. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that an excited atom emits light only at specific, discrete wavelengths (a line spectrum), rather than a continuous range of wavelengths.
- Identifies the missing requirement: States that each spectral line corresponds to a photon of a specific energy, emitted when an electron falls from a higher energy level to a lower one.
- Identifies the missing requirement: States that since only specific photon energies (and hence wavelengths) are observed, the electron energy levels themselves must be discrete (quantised), not continuous.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
19.
A nucleus of nitrogen-14 undergoes a nuclear reaction, absorbing an alpha particle and emitting a proton, producing an isotope of oxygen. Write the balanced nuclear equation for this reaction.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: Writes the reactants: ₇¹⁴N + ₂⁴He. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Work through this mathematical step: Balances mass number: 14 + 4 = 18, and atomic number: 7 + 2 = 9, so the products must total mass number 18 and atomic number 9. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
4. Work through this mathematical step: Writes the balanced equation: ₇¹⁴N + ₂⁴He → ₈¹⁷O + ₁¹H, confirming mass numbers (14+4=17+1) and atomic numbers (7+2=8+1) balance. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: In any nuclear equation, both the total mass number and the total atomic number must be equal on both sides — use this as a check after balancing.
Marking points
- Writes the reactants: ₇¹⁴N + ₂⁴He.
- Balances mass number: 14 + 4 = 18, and atomic number: 7 + 2 = 9, so the products must total mass number 18 and atomic number 9.
- Writes the balanced equation: ₇¹⁴N + ₂⁴He → ₈¹⁷O + ₁¹H, confirming mass numbers (14+4=17+1) and atomic numbers (7+2=8+1) balance.
Examiner tip: In any nuclear equation, both the total mass number and the total atomic number must be equal on both sides — use this as a check after balancing.
20.
Marking analysis: A learner attempts the following task: “A nucleus of nitrogen-14 undergoes a nuclear reaction, absorbing an alpha particle and emitting a proton, producing an isotope of oxygen. Write the balanced nuclear equation for this reaction.” Their response addresses only this point: “Writes the reactants: ₇¹⁴N + ₂⁴He.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: Writes the reactants: ₇¹⁴N + ₂⁴He. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Balances mass number: 14 + 4 = 18, and atomic number: 7 + 2 = 9, so the products must total mass number 18 and atomic number 9. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Writes the balanced equation: ₇¹⁴N + ₂⁴He → ₈¹⁷O + ₁¹H, confirming mass numbers (14+4=17+1) and atomic numbers (7+2=8+1) balance. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: Writes the reactants: ₇¹⁴N + ₂⁴He.
- Identifies the missing requirement: Balances mass number: 14 + 4 = 18, and atomic number: 7 + 2 = 9, so the products must total mass number 18 and atomic number 9.
- Identifies the missing requirement: Writes the balanced equation: ₇¹⁴N + ₂⁴He → ₈¹⁷O + ₁¹H, confirming mass numbers (14+4=17+1) and atomic numbers (7+2=8+1) balance.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
21.
A helium-4 nucleus has a mass of 4.001505 u. Its constituent 2 protons (1.00728 u each) and 2 neutrons (1.00867 u each) have a combined mass of 4.03190 u. Calculate the mass defect and the binding energy of the helium-4 nucleus. Use 1 u = 931.5 MeV/c².
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Calculates the mass defect: Δm = 4.03190 − 4.001505 = 0.030395 u. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
3. Work through this mathematical step: States that binding energy = Δmc². Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
4. Work through this mathematical step: Converts using 1 u = 931.5 MeV/c²: BE = 0.030395 × 931.5. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Develop this part of the answer: Obtains BE ≈ 28.3 MeV. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The mass of a nucleus is always slightly less than the sum of the masses of its separate constituent protons and neutrons — this 'missing' mass, the mass defect, is exactly what has been converted into the binding energy holding the nucleus together.
Marking points
- Calculates the mass defect: Δm = 4.03190 − 4.001505 = 0.030395 u.
- States that binding energy = Δmc².
- Converts using 1 u = 931.5 MeV/c²: BE = 0.030395 × 931.5.
- Obtains BE ≈ 28.3 MeV.
Examiner tip: The mass of a nucleus is always slightly less than the sum of the masses of its separate constituent protons and neutrons — this 'missing' mass, the mass defect, is exactly what has been converted into the binding energy holding the nucleus together.
22.
Marking analysis: A learner attempts the following task: “A helium-4 nucleus has a mass of 4.001505 u. Its constituent 2 protons (1.00728 u each) and 2 neutrons (1.00867 u each) have a combined mass of 4.03190 u. Calculate the mass defect and the binding energy of the helium-4 nucleus. Use 1 u = 931.5 MeV/c².” Their response addresses only this point: “Calculates the mass defect: Δm = 4.03190 − 4.001505 = 0.030395 u.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: Calculates the mass defect: Δm = 4.03190 − 4.001505 = 0.030395 u. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that binding energy = Δmc². Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Converts using 1 u = 931.5 MeV/c²: BE = 0.030395 × 931.5. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: Obtains BE ≈ 28.3 MeV. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: Calculates the mass defect: Δm = 4.03190 − 4.001505 = 0.030395 u.
- Identifies the missing requirement: States that binding energy = Δmc².
- Identifies the missing requirement: Converts using 1 u = 931.5 MeV/c²: BE = 0.030395 × 931.5.
- Identifies the missing requirement: Obtains BE ≈ 28.3 MeV.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
23.
Cobalt-60 (₂₇⁶⁰Co) undergoes beta-minus decay. Write the balanced nuclear equation for this decay, identifying the emitted particle.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that in beta-minus decay, a neutron in the nucleus converts into a proton, emitting an electron (a beta particle). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that mass number remains unchanged (60), while atomic number increases by 1 (27 → 28). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Work through this mathematical step: Writes the balanced equation: ₂₇⁶⁰Co → ₂₈⁶⁰Ni + ₋₁⁰e. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Cobalt-60's decay to nickel-60 with gamma emission accompanying the beta decay is a real isotope widely used in radiotherapy and industrial gamma radiography.
Marking points
- States that in beta-minus decay, a neutron in the nucleus converts into a proton, emitting an electron (a beta particle).
- States that mass number remains unchanged (60), while atomic number increases by 1 (27 → 28).
- Writes the balanced equation: ₂₇⁶⁰Co → ₂₈⁶⁰Ni + ₋₁⁰e.
Examiner tip: Cobalt-60's decay to nickel-60 with gamma emission accompanying the beta decay is a real isotope widely used in radiotherapy and industrial gamma radiography.
24.
Marking analysis: A learner attempts the following task: “Cobalt-60 (₂₇⁶⁰Co) undergoes beta-minus decay. Write the balanced nuclear equation for this decay, identifying the emitted particle.” Their response addresses only this point: “States that in beta-minus decay, a neutron in the nucleus converts into a proton, emitting an electron (a beta particle).” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that in beta-minus decay, a neutron in the nucleus converts into a proton, emitting an electron (a beta particle). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that mass number remains unchanged (60), while atomic number increases by 1 (27 → 28). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Writes the balanced equation: ₂₇⁶⁰Co → ₂₈⁶⁰Ni + ₋₁⁰e. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that in beta-minus decay, a neutron in the nucleus converts into a proton, emitting an electron (a beta particle).
- Identifies the missing requirement: States that mass number remains unchanged (60), while atomic number increases by 1 (27 → 28).
- Identifies the missing requirement: Writes the balanced equation: ₂₇⁶⁰Co → ₂₈⁶⁰Ni + ₋₁⁰e.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
25.
Explain what is meant by the random and spontaneous nature of radioactive decay, and state why it is impossible to predict when a specific individual nucleus will decay.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that radioactive decay is spontaneous: it is not affected by external conditions such as temperature, pressure or chemical state. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that it is random: each individual nucleus has the same constant probability of decaying in a given time interval, regardless of its age or history. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that because of this randomness, it is impossible to predict exactly when any single specific nucleus will decay — only the average behaviour of a very large number of nuclei, described by the half-life, can be predicted statistically. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: A nucleus has no 'memory' of how long it has already existed — an old undecayed nucleus is exactly as likely to decay in the next second as a newly formed one of the same isotope.
Marking points
- States that radioactive decay is spontaneous: it is not affected by external conditions such as temperature, pressure or chemical state.
- States that it is random: each individual nucleus has the same constant probability of decaying in a given time interval, regardless of its age or history.
- States that because of this randomness, it is impossible to predict exactly when any single specific nucleus will decay — only the average behaviour of a very large number of nuclei, described by the half-life, can be predicted statistically.
Examiner tip: A nucleus has no 'memory' of how long it has already existed — an old undecayed nucleus is exactly as likely to decay in the next second as a newly formed one of the same isotope.
26.
Marking analysis: A learner attempts the following task: “Explain what is meant by the random and spontaneous nature of radioactive decay, and state why it is impossible to predict when a specific individual nucleus will decay.” Their response addresses only this point: “States that radioactive decay is spontaneous: it is not affected by external conditions such as temperature, pressure or chemical state.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that radioactive decay is spontaneous: it is not affected by external conditions such as temperature, pressure or chemical state. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that it is random: each individual nucleus has the same constant probability of decaying in a given time interval, regardless of its age or history. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that because of this randomness, it is impossible to predict exactly when any single specific nucleus will decay — only the average behaviour of a very large number of nuclei, described by the half-life, can be predicted statistically. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that radioactive decay is spontaneous: it is not affected by external conditions such as temperature, pressure or chemical state.
- Identifies the missing requirement: States that it is random: each individual nucleus has the same constant probability of decaying in a given time interval, regardless of its age or history.
- Identifies the missing requirement: States that because of this randomness, it is impossible to predict exactly when any single specific nucleus will decay — only the average behaviour of a very large number of nuclei, described by the half-life, can be predicted statistically.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
27.
Sodium-22 (₁₁²²Na) decays by beta-plus (positron) emission. Write the balanced nuclear equation for this decay, and state what happens to the mass number and atomic number.
[4 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States that in beta-plus decay, a proton in the nucleus converts into a neutron, emitting a positron. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that the mass number remains unchanged (22). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that the atomic number decreases by 1 (11 → 10). Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Work through this mathematical step: Writes the balanced equation: ₁₁²²Na → ₁₀²²Ne + ₊₁⁰e. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Beta-plus decay is the mirror image of beta-minus decay: atomic number decreases instead of increasing, and a positron (matter's antiparticle counterpart to the electron) is emitted instead of an electron.
Marking points
- States that in beta-plus decay, a proton in the nucleus converts into a neutron, emitting a positron.
- States that the mass number remains unchanged (22).
- States that the atomic number decreases by 1 (11 → 10).
- Writes the balanced equation: ₁₁²²Na → ₁₀²²Ne + ₊₁⁰e.
Examiner tip: Beta-plus decay is the mirror image of beta-minus decay: atomic number decreases instead of increasing, and a positron (matter's antiparticle counterpart to the electron) is emitted instead of an electron.
28.
Marking analysis: A learner attempts the following task: “Sodium-22 (₁₁²²Na) decays by beta-plus (positron) emission. Write the balanced nuclear equation for this decay, and state what happens to the mass number and atomic number.” Their response addresses only this point: “States that in beta-plus decay, a proton in the nucleus converts into a neutron, emitting a positron.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States that in beta-plus decay, a proton in the nucleus converts into a neutron, emitting a positron. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that the mass number remains unchanged (22). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that the atomic number decreases by 1 (11 → 10). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: Writes the balanced equation: ₁₁²²Na → ₁₀²²Ne + ₊₁⁰e. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States that in beta-plus decay, a proton in the nucleus converts into a neutron, emitting a positron.
- Identifies the missing requirement: States that the mass number remains unchanged (22).
- Identifies the missing requirement: States that the atomic number decreases by 1 (11 → 10).
- Identifies the missing requirement: Writes the balanced equation: ₁₁²²Na → ₁₀²²Ne + ₊₁⁰e.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
29.
State one medical use of a radioactive isotope, and explain why gamma-emitting isotopes with short half-lives are generally preferred for use as internal medical tracers.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
2. Develop this part of the answer: States a valid use, e.g. as a tracer to monitor organ function, or in the treatment of cancerous tumours. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Develop this part of the answer: States that gamma radiation is used because it can penetrate the body and be detected externally, without causing as much internal ionising damage as alpha or beta radiation would. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Develop this part of the answer: States that a short half-life is preferred so that the isotope decays away quickly, minimising the patient's total radiation dose and exposure time. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The ideal medical tracer isotope balances two competing needs: it must last long enough to complete the diagnostic procedure, but decay away quickly afterwards to minimise the patient's long-term radiation exposure.
Marking points
- States a valid use, e.g. as a tracer to monitor organ function, or in the treatment of cancerous tumours.
- States that gamma radiation is used because it can penetrate the body and be detected externally, without causing as much internal ionising damage as alpha or beta radiation would.
- States that a short half-life is preferred so that the isotope decays away quickly, minimising the patient's total radiation dose and exposure time.
Examiner tip: The ideal medical tracer isotope balances two competing needs: it must last long enough to complete the diagnostic procedure, but decay away quickly afterwards to minimise the patient's long-term radiation exposure.
30.
Marking analysis: A learner attempts the following task: “State one medical use of a radioactive isotope, and explain why gamma-emitting isotopes with short half-lives are generally preferred for use as internal medical tracers.” Their response addresses only this point: “States a valid use, e.g. as a tracer to monitor organ function, or in the treatment of cancerous tumours.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
2. Requirement 1: Recognises credit for the stated point: States a valid use, e.g. as a tracer to monitor organ function, or in the treatment of cancerous tumours. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that gamma radiation is used because it can penetrate the body and be detected externally, without causing as much internal ionising damage as alpha or beta radiation would. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that a short half-life is preferred so that the isotope decays away quickly, minimising the patient's total radiation dose and exposure time. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.
Marking points
- Recognises credit for the stated point: States a valid use, e.g. as a tracer to monitor organ function, or in the treatment of cancerous tumours.
- Identifies the missing requirement: States that gamma radiation is used because it can penetrate the body and be detected externally, without causing as much internal ionising damage as alpha or beta radiation would.
- Identifies the missing requirement: States that a short half-life is preferred so that the isotope decays away quickly, minimising the patient's total radiation dose and exposure time.
Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.